[Pool] Score is drop in cycles
rob at knoware.nl
Fri Feb 21 09:52:21 UTC 2014
Jeff Woolsey wrote:
> On 02/20/14 12:21, Timothy Oefelein wrote:
>> One of the these days I'd like to get the hardware to run my own Stratum 1 server, which would make the whole finding peers process moot. :)
> Not necessarily. Trust but verify your local reference clock against other servers out there. For example, I'm currently seeing about 60ms of jitter/offset in the SHM refclock from gpsd managing a SiRF II device. (It was 10 seconds off before I
> fixed gpsd not to request messages it's ignoring anyway.). It's USB, but still I'd expect only 1-2ms of offset/jitter, which is fine for my purposes:
Using serial messages as a timesync (other than for determining the time in seconds) is no good.
There is no good lock between the timing of the serial messages relative to the real time value in them.
And when there is other traffic on the line, this becomes even more apparent.
(not a 10 second difference though, you must have other issues!)
Serial message sources wandering around 60ms relative to the correct time are quite common. Can be even more!
To have any value from a local GPS receiver, you need to use PPS.
This was easy in the days of RS232. I have a GPS module on a real RS232 port (not USB) with PPS connected to DCD and timesync via gpsd.
It shows 0.001 in the jitter column. It would be even better with a newer kernel that supports PPS in the kernel so it does not have to be handled in the gpsd user process.
But GPS with only serial and no PPS - forget it. External sources on a good internet connection will be better.
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